1. Field of the Invention
The present invention relates generally to the use of antibodies for treatment and diagnosis of diseases, most notably tumors and cancerous lesions. More particularly it relates to the modification and use of cationized antibodies for transport through capillary barriers into the interstitial fluid of organs.
2. Description of Related Art
Antibodies in general, and especially monoclonal antibodies, are widely used in diagnostic tests as a means for detecting the presence of specific antigens and in the treatment of diseases associated with a specific antigen. More particularly, antibodies have been used as targeting vehicles for radioisotopes, magnetic resonance imaging agents, toxins and cytotoxic drugs, especially in the diagnosis and treatment of cancer, tumors, and certain infectious diseases.
Enzyme linked immunoassay and radioimmunoassay are common diagnostic techniques which utilize antibodies as targeting vehicles and detect antigens in vitro. Antigens may also be detected in vivo by administering radio labelled or paramagnetic labelled antibodies to a living subject followed by the external detection of the radio labelled antibody sequestered by a particular organ bearing the respective antigen.
One of the limitations in using antibodies as targeting vehicles in either the in vivo treatment or diagnosis of cancer and infectious diseases has been the inability to obtain effective concentrations of the targeting antibody at the target site. The low antibody dose at the site is largely due to poor antibody uptake by the tumor or infected site. The poor uptake is due to the microvascular or endothelial barrier which is present in most organs. This endothelial barrier has pores which are too small to allow for rapid organ uptake of circulating antibodies. Also the small size of the aqueous pores in the walls of the vessels which perfuse organs greatly restricts antibody transport from the vessels into the organ.
Transport across the endothelial barrier is a particular problem for large plasma proteins, such as antibodies that have molecular weights in excess of 150,000 Daltons. These antibodies are excluded or cross the microvascular barrier only very slowly. Not only does the size of these large antibodies restrict their transport across the endothelial barrier, but, their electrical charges also present transport problems. More specifically, the molecules on the surface of capillaries are anionically charged and, therefore, present an electrical barrier to the neutral or slightly negatively charged antibodies.
Another limitation to an optimum concentration of targeting antibody at the target organ site is the higher permeability of the liver and spleen vascular barrier. The liver and spleen do not exclude the transport of large molecules to the same degree as other organs. Consequently, these two organs will preferentially remove administered antibodies from the blood leaving only a small concentration for therapeutic or diagnostic delivery to other organs.
Since most of the radioisotopes or complexes used in targeting systems are somewhat toxic and dose limiting, merely increasing the dose of the antibody with the expectation that more will become available to the organ of interest is not a practical solution.
Strategies have been developed to administer effective amounts of antibodies by an invasive regional route to the location of the tumor or diseased area. This avoids a high concentration of a potentially toxic agent in the blood. For systemic administration, however, it is necessary to use methods which control or enhance the blood clearance of the targeted antibodies. Such techniques aid in avoiding toxic blood levels of radioisotopes or other therapeutic agents, but still require large doses of the antibody because of their restricted transport across capillary barriers.
Accordingly there presently is a need to provide an improved method for the diagnosis and treatment of cancer and infectious diseases which are responsive to antibodies used as target vehicles. Further, there is a need to provide improved methods for delivering effective amounts of antibodies to organ tissue without sustaining toxic amounts of the antibody target vehicle in the blood. There is also a need to provide improved means for transporting antibodies across the microvascular barrier of organs and into the interstitial pores of organs.